E-textiles fabricated using particle-free conductive inks

ABSTRACT

Described herein are methods for forming e-textiles, wherein the methods include printing a particle-free conductive ink on a textile substrate, and curing the textile substrate to produce a conductive pattern thereon. The printing may include inkjet printing and may produce a printed pattern which exhibits an ink bleed of less than 0.5 mm, such as less than 0.2 mm. During printing, the textile substrate may be heated to a temperature of 30° C. to 90° C. before and during the printing process. The fabric substrate may be cured using heat and/or light to produce a conductive pattern having a sheet resistance of less than 10 Ω/□, or even less than 1 Ω/□.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/275,161, filed Feb. 13, 2019, which claims the benefit under35 U.S.C. § 119(e) of prior U.S. Provisional Application Ser. No.62/630,005, filed Feb. 13, 2018; 62/674,864, filed May 22, 2018; and62/745,710, filed Oct. 15, 2018, the entire contents of which areincorporated herein.

TECHNICAL FIELD

This invention pertains generally to methods for printing particle-freeconductive inks on textiles and e-textiles having conductive patternsprinted thereon.

BACKGROUND

Electronic textiles (“e-textiles”) are known and used as wearabletechnologies that provide electronic elements built directly into thetextile, such as into an article of clothing. E-textiles have a widevariety of uses in the fields of biomedicine, sports, military, andenergy harvesting. Known e-textiles are not without disadvantageshowever. For example, elements of the wearable devices are typicallyconnected by cables and various connectors which can be snagged or mayinterfere with normal use of the fabric or garment. Additionally, thevarious components of the e-textiles are often not easily cleaned.

Knitting, weaving, and embroidery of conductive threads have been usedto solve some of these problems, but such solutions are generally notscalable or easy to manufacture. Moreover, these fabrics tend to berough and/or porous due to incorporation of the conductive threads.Conductive metal coatings and screen printing have also been used toincorporate conductive patterns on textiles, with some difficultiesrelated to achieving a continuous conductive path on differing textilesubstrates.

Printed electronics is one of the fastest growing technologies in theworld, providing integration of complex electronic functionality into awide range of products. Inks and methods of printing those inks ontextiles has, however, lagged behind. Suitable inks are essential forthe manufacture of these printed electronics, with conductive inksconsidered the most important materials for a variety of electrodes(including transparent electrodes). In general, electronic inks composedof conductive metal nanoparticles are used to print (or coat) asubstrate using a range of printing systems, such as a gravure printing,flexographic printing, (rotary) screen printing, offset printing,gravure-offset printing, microdispersion, direct write printing, or(nano)imprinting system. This is followed by drying or sintering to forma metal wire with a desired shape. While these inks offer a solution tosome of the difficulties with prior art methods for providing conductivepaths on substrates such as glass, they are generally not suitable fortextiles that may melt or deform at the high sintering temperaturesemployed in curing the inks.

Moreover, these inks frequently suffer from poor long-term storagestability and/or undergo aggregation or precipitation of the particles,causing nozzle clogging when using certain printing methods. Polymericmaterials have been used as stabilizers to circumvent such problems.However, excessive use of the stabilizers increases the viscosity of theinks or causes other problems, such as increased surface tension, highersintering temperatures, and decreased conductivity.

One approach to solve some of these problems with the nanoparticle inksis to use organometallic salts or complexes as metal precursors.However, silver-containing carboxylic acid salts are generally notreadily soluble and have high decomposition temperatures, which limittheir applicability. Attempts to solve such problems have been made, forexample, by the use of silver precursors in which an electron donor,such as an amine or phosphine compound, is coordinated to a fluorinatedcarboxylic acid. Such metal complex inks have low metal solids contentand/or also suffer from poor storage stability, which limit theirapplication in products where highly reliable and conductive metaltraces are needed.

Accordingly, there is a need in the art for improved inks and methodsfor printing those inks on textiles to produce e-textiles.

SUMMARY

Described herein are methods for forming e-textiles, wherein the methodsgenerally comprise printing a particle-free conductive ink on a textilesubstrate, and curing the textile substrate to produce a conductivepattern thereon. According to certain aspects of the invention, curingthe textile substrate may be accomplished by exposing the textilesubstrate to heat and/or light. For example, the textile substrate maybe cured by exposure to heat, such as at temperatures of less than 250°C., or less than 200° C., or less than 150° C. Alternatively, or inaddition, curing may include irradiating the textile substrate, such asby exposure to 2 to 20 pulses of light, e.g., photonic curing, or mayinclude exposure to infrared radiation. Once cured, the conductivepattern on the textile substrate may have a sheet resistance as low as1Ω/□ or even lower.

According to certain aspects of the invention, the textile substrate maybe heated to a temperature of 30° C. to 90° C. before and/or during theprinting process, such as 30° C. to 60° C., or 40° C. to 90° C. beforeand/or during the printing process.

Printing on the substrate may be via flexographic printing, gravureprinting, gravure offset printing, rotary screen process printing,pneumatic aerosol jet printing, ultrasonic aerosol jet printing,extrusion printing, slot die printing, microdispersion, direct writeprinting, inkjet printing or a combination. According to certain aspectsof the present invention, the conductive ink may be printed via inkjetprinting and the method may produce a printed pattern that exhibits anink bleed of less than 0.5 mm, such as less than 0.2 mm, or even lessthan 0.1 mm.

According to certain aspects of the invention, the pattern may includeone or more layers of the particle-free conductive ink, such as at least2 layers, or at least 4 layers, or at least 6 layers or more of theparticle-free conductive ink.

The substrate may include polymers, organic and synthetic fibers,plastics, metals, ceramics, glasses, silicon, semiconductors, and othersolids can be used. Organic and inorganic substrates can be used.According to certain aspects of the invention, the substrate may be atextile such as a knit, woven, or nonwoven textile or fabric formed oforganic or synthetic fibers. Exemplary fibers of such textile substratesinclude at least polyester, polyamides, nylon, Evolon®, elastane, andother synthetic materials, in addition to organic materials (e.g.,cotton, cellulose, silk, wood, wool fibers).

The conductive pattern printed on the textile substrate may comprise asensor, an electrode, a trace, an antenna, a heating element, or anycombination thereof.

The particle-free conductive ink may comprise at least one metal complexdissolved in a solvent, wherein the at least one metal complex comprisesat least one metal, at least one first ligand, and at least one secondligand. Exemplary metals include silver, gold, or copper. Exemplaryfirst ligands include amines and sulfur containing compounds, andexemplary second ligands include carboxylic acids, dicarboxylic acids,and tricarboxylic acids. Exemplary solvents include one or more polarprotic solvents, such as at least two polar protic solvents selectedfrom the group comprising at least water, alcohols, amines, aminoalcohols, polyols, and combinations thereof.

The metal complexes may have a solubility at 25° C. in the solvent of atleast 50 mg/ml, or at least 250 mg/ml, or at least 500 mg/ml, or atleast 1,000 mg/ml, or at least 1,500 mg/ml, or at least 2,000 mg/ml.

The present invention is also directed to methods of forming aconductive pattern. According to certain aspects of the invention, themethod comprises depositing the particle-free conductive inks detailedherein on a substrate, and curing the substrate to produce a conductivepattern having a conductivity of at least 1,000 S/m, such as at least5,000 S/m, or at least 10,000 S/m, or at least 50,000 S/m, or at least100,000 S/m, or at least 1,000,000 Sm, or at least 10,000,000 S/m, oreven 2×10⁷ S/m.

According to certain aspects of the invention, the first and secondligands volatilize upon heat at a temperature of 250° C. or less, 200°C. or less, or even 150° C. or less, so that the curing may be at atemperature of 250° C. or less, 200° C. or less, or even 150° C. orless.

According to certain aspects of the invention, curing the substrate mayadditionally or alternatively comprises irradiating the substrate for atime period of not more than 15 minutes. Irradiating the substrate mayinclude exposure to pulsed light, such as from 2 to 20 pulses of light,and/or infrared radiation.

Also disclosed are e-textiles formed by the methods of the presentinvention, and wearable electronic devices comprising the e-textiles.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects, features, benefits and advantages of the embodiments hereinwill be apparent with regard to the following description, appendedclaims, and accompanying drawings. In the following figures, likenumerals represent like features in the various views. It is to be notedthat features and components in these drawings, illustrating the viewsof embodiments of the presently disclosed invention, unless stated to beotherwise, are not necessarily drawn to scale.

FIGS. 1A-1C illustrate prior art methods for incorporating conductivematerials to a textile, such as by incorporating conductive threads;

FIG. 2 illustrates a prior art method for incorporating conductivetraces between insulating or protective layers;

FIG. 3 illustrates a wearable electronic device which incorporates theconductive traces of the prior art shown in FIG. 2 ;

FIGS. 4A-4E illustrate aspects of the prior art nanoparticle inksprinted on a non-woven textile, where FIGS. 4A and 4B show two differentmagnifications of scanning electron micrograph (SEM) images of a singlelayer of nanoparticle silver ink printed on Evolon®; FIG. 4C is a crosssectional view SEM image of the same textile, wherein the fibers arecolored green and the nanoparticle silver ink is shown in red; FIG. 4Dshows the distribution of the nanoparticle silver ink throughout thetextile shown in FIG. 4C (i.e., only the nanoparticle silver ink isshown); and FIG. 4E shows resistance readings for 2 to 5 layers ofnanoparticle inks printed on Evolon® or modified Evolon®;

FIGS. 4F and 4G are schematic diagrams showing the coating of textilefibers by a nanoparticle ink of the prior art and conformal coating oftextile fibers by the particle-free inks of the presently disclosedinvention, respectively;

FIG. 5 illustrates knit textiles screen-printed with conductivematerials of the prior art under different amounts of strain (i.e.,stretch of the textile);

FIG. 6 illustrates an inkjet printer setup useful in methods of thepresently disclosed invention;

FIGS. 7A and 7B show photographs of the front and back, respectively, ofa nonwoven textile having a conductive pattern printed thereon inaccordance with certain aspects of the presently disclosed invention;

FIG. 8A shows a woven textile having a conductive ink according tocertain aspects of the presently disclosed invention conformally coatedon a portion thereof (coated at left; uncoated at right), and FIGS. 8Band 8C show close-up SEM views of the coated portions of the textile(150× and 800× magnification, respectively);

FIG. 9 shows a proton nuclear magnetic resonance (¹H-NMR) scan of anexemplary metal complex (ethylenediaminosilver(I) isobutyrate in D₂O)according to certain aspects of the presently disclosed invention, and(upper right) the structure of an exemplary conductive ink of thepresent invention;

FIG. 10 shows a proton nuclear magnetic resonance (¹H-NMR) scan of anexemplary particle-free conductive ink (ethylenediaminosilver(I)isobutyrate dissolved in polar protic solvents and in D₂O) according tocertain aspects of the presently disclosed invention;

FIG. 11 shows a graph of the resistance (ohms) after multiple washcycles for a conductive trace on a textile using inks and methods inaccordance with certain aspects of the presently disclosed invention;

FIG. 12 shows a graph of the change in resistance with increased strain(stretch) for a conductive trace on a textile using inks and methods inaccordance with certain aspects of the presently disclosed invention;

FIG. 13 shows a graph of the change in resistance with increased bendingcycles for a conductive trace on a textile using inks and methods inaccordance with certain aspects of the presently disclosed invention;

FIG. 14 shows a picture of an e-textile proximity sensor printed usinginks and methods in accordance with certain aspects of the presentlydisclosed invention;

FIG. 15 shows a schematic diagram of an exemplary 5-trace heater elementin accordance with certain aspects of the presently disclosed invention,wherein the numbered blocks are test locations for resistancemeasurements;

FIG. 16A shows a graph of resistance measurements from 5-trace heatersformed according to certain aspects of the presently disclosedinvention, wherein the readings were taken at the locations indicated inFIG. 15 , data is normalized to 1.0 for location 36, and FIG. 16B showsthe deviation of the data shown in FIG. 16A from the expected value(dotted lines in FIG. 16A);

FIGS. 17A and 17B show series and parallel circuits, respectively, of5-trace heaters formed according to certain aspects of the presentlydisclosed invention; and

FIGS. 18A-18C show graphs demonstrating the linearity of temperatureincrease with power increase (FIG. 18A), and the lack of resistancedrift over time or temperature (FIGS. 18B and 18C, respectively) for5-trace heaters formed according to certain aspects of the presentlydisclosed invention.

DETAILED DESCRIPTION

In the following description, the present invention is set forth in thecontext of various alternative embodiments and implementations involvingparticle-free conductive inks, methods for printing these inks ontextiles, and e-textiles having these inks printed thereon. While thefollowing description discloses numerous exemplary embodiments, thescope of the present patent application is not limited to the disclosedembodiments, but also encompasses combinations of the disclosedembodiments, as well as modifications to the disclosed embodiments.

Various aspects of the particle-free conductive inks and e-textilesdisclosed herein may be illustrated by describing components that arecoupled, attached, and/or joined together. As used herein, the terms“coupled”, “attached”, and/or “joined” are interchangeably used toindicate either a direct connection between two components or, whereappropriate, an indirect connection to one another through interveningor intermediate components. In contrast, when a component is referred toas being “directly coupled”, “directly attached”, and/or “directlyjoined” to another component, there are no intervening elements shown insaid examples.

Various aspects of the inks, e-textiles, and methods disclosed hereinmay be described and illustrated with reference to one or more exemplaryimplementations. As used herein, the term “exemplary” means “serving asan example, instance, or illustration,” and should not necessarily beconstrued as preferred or advantageous over other variations of thedevices, systems, or methods disclosed herein. “Optional” or“optionally” means that the subsequently described event or circumstancemay or may not occur, and that the description includes instances wherethe event occurs and instances where it does not. In addition, the word“comprising” as used herein means “including, but not limited to”.

Relative terms such as “lower” or “bottom” and “upper” or “top” may beused herein to describe one element's relationship to another elementillustrated in the drawings. It will be understood that relative termsare intended to encompass different orientations of aspects of thee-textiles disclosed herein in addition to the orientation depicted inthe drawings. By way of example, if aspects of the e-textiles in thedrawings are turned over, elements described as being on the “bottom”side of the other elements would then be oriented on the “top” side ofthe other elements as shown in the relevant drawing. The term “bottom”can therefore encompass both an orientation of “bottom” and “top”depending on the particular orientation of the drawing.

It must also be noted that as used herein and in the appended claims,the singular forms “a”, “an”, and “the” include the plural referenceunless the context clearly dictates otherwise. For example, althoughreference is made to “a” textile, “an” upper layer, “a” metal, “an” ink,and “the” metal complex, one or more of any of these components and/orany other components described herein can be used.

Moreover, other than in any operating examples, or where otherwiseindicated, all numbers expressing, for example, quantities ofingredients used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and appended claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard variation found in theirrespective testing measurements.

“Substantially free”, as used herein, is understood to mean inclusive ofonly trace amounts of a constituent. “Trace amounts” are thosequantitative levels of a constituent that are barely detectable andprovide no benefit to the functional properties of the subjectcomposition, process, or articles formed therefrom. For example, a traceamount may constitute 1.0 wt. %, 0.5 wt. %, 0.1 wt. %, 0.05 wt. %, oreven 0.01 wt. % of a component of any of the particle-free inkformulations disclosed herein. “Totally free”, as used herein, isunderstood to mean completely free of a constituent.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art.

The present invention provides methods for printing particle-freeconductive inks on textiles to form e-textiles. These e-textiles mayfind use in a range of different applications, including at leastwearable sensors for fitness and health monitoring, gas sensors andfilters for use in industrial applications, antimicrobial dressings foruse in medical applications, flexible energy storage devices, heatingelements, and communication devices.

Certain prior art e-textiles have included conductive elements as partof the yarn used to form the textile, such as shown in FIGS. 1A-1C. Forexample, conductive metal threads have been woven with standard organic,polymeric, or synthetic threads to form conductive yarns, which can thenbe used to produce a textile. FIG. 1A shows a metal wrapped yarn, FIG.1B shows a metal filled yarn, and FIG. 1C shows a metal yarn (i.e., yarnformed wholly of metal threads or wire). These textiles tend to be roughand/or porous, and can be costly due to the expense of the conductivematerials (generally metals). These costs can be reduced by using theyarns to produce specific conductive patterns in the textile, but thisgenerally requires changes to manufacturing processes that are noteasily altered.

Alternatively, conductive patterns have been incorporated on flexiblesubstrates (FIG. 2 ), which are then adhered to the textile to formwearable electronics (FIG. 3 ). These patterns may not be stretchableand/or washable, and application of the patterns may require additionalmanual and/or manufacturing processes.

Direct print methods have been used to form conductive patterns. Suchmethods would be easily scalable, easily integrated into current textilemanufacturing processes, and provide a high throughput, highly automatedmeans to provide conductive elements, and thus electronic elements intotextiles. The conductive inks of the prior art, however, often do notshow good results. For example, inkjet printing with nanoparticle inkshas proven challenging due to clogging of the nozzle and either toolittle interaction with the textile surface, e.g., pooling, or too muchinteraction with the textile surface, e.g., spreading due to capillaryeffects. As shown in FIGS. 4A and 4B, for example, nanoparticle inksprinted on nonwoven textiles such as Evolon® can pool, failing to coatthe fibers to the extent required to form a conductive pattern. Evenafter multiple layers are applied, such as the 6 layers of ink shown inFIGS. 4C and 4D, scanning electron micrograph images show that the inkis pooled into islands separated by non-coated areas. For example, FIGS.4C and 4D show that the Evolon® non-woven fiber (green) includes the ink(red dots) discontinuously on the top (FIG. 4C) and throughout thethickness of the textile via capillary spreading (FIG. 4D).

As shown in FIG. 4E, because these nanoparticle inks fail to form acontinuous pattern, they demonstrate extremely high resistance (i.e.,fail to form conductive traces). Moreover, additional coating layers ofthe nanoparticle inks does not reduce the resistance of these printedpatterns. Modification of the textile to decrease surface resistance ispossible, such as up to 2 orders of magnitude, but still does not formconductive patterns (FIG. 4E at right). The red dots on the greenbackground in FIGS. 4C and 4D represent clustered silver particles withlittle silver-to-silver fusion or connectivity; hence the poorconductivity of silver nanoparticle films (see FIG. 4F). The poorconductivity is further worsened by the low temperature limitation ofmost textile substrates, such as fabrics, which makes it impossible tosystematically fuse silver particles with the high temperatures oftenrequired for nanoparticle ink curing.

Patterns formed on textiles with nanoparticle inks generally show poorflexibility during use of the textile (e.g., multiple wear and/or washcycles). As illustrated in FIG. 5 , strain such as by stretching ascreen printed woven textile leads to breaks in the conductive pattern,rendering the pattern non-conductive over time. In fact, as little as10% strain on the textile can lead to an observable increase in breaksin the printed pattern and loss of conductivity.

The inventive processes disclosed herein circumvent many of thesedifficulties by directly printing a pattern on the textile usingparticle-free conductive inks, and thus provide highly scalable andautomated methods for producing e-textiles. The methods generallycomprise using a direct printing process, such as inkjet printing, todeposit a particle-free conductive ink on the textile substrate, whichis then cured to produce a conductive pattern thereon. As such, theconductive patterns may be formed on the textile, or on the finalwearable product, in a manner that is easily integrated into currentmanufacturing processes, and more importantly, is easily scalable andcan be highly automated. Moreover, the methods disclosed herein provideconformal coating of the particle-free ink on the textile fibers (FIG.4G) that allows for greatly improved conductivity and longevity of theconductive trace. As used herein, the term “conformal” shall be taken tomean a coating that covers at least the surface of a textile, fiber, orsubstrate, and which follows the contours of the surface.

Particle-Free Conductive Inks

The particle-free conductive inks of the present invention generallyinclude a metal complex dissolved in a solvent. The metal complex can bemononuclear, dinuclear, trinuclear, and higher. For example, the metalcomplex may be a neutral metal complex comprising at least one metal, atleast one first ligand, and at least one second ligand. The metalcomplex may be as described in US Patent Application Publications2011/0111138 and 2013/0236656. The metal complex may comprise a firstmetal complex having at least one first metal, and a second metalcomplex having at least one second metal. The metal complex may be asdescribed in U.S. Pat. No. 9,920,212.

For example, according to certain aspects of the present invention, aneutral metal complex may be formed by first forming a complex betweenthe metal (M) and the second ligand (L₂), such as by reacting a metal,metal salt, or metal oxide with the second ligand. The metal-secondligand complex may then be reacted with an excess of the first ligand(L₁) to form the neutral metal complex. The stoichiometric reactionratio between the first ligand and the metal-second ligand complex canbe, for example, at least 2:1, such as at least 5:1, or at least 10:1,or at least 13:1, or at least 15:1, or at least 20:1. When formulated inthis way, the reaction mixture remains substantially or totally free ofparticles, and progresses to completion forming a metal complex havingstoichiometric amounts of the first and second ligands and the metal.

The excess, unreacted first ligand may be removed to provide the metalcomplex having stoichiometric amounts of the metal, first ligand, andsecond ligand (i.e., free of unliganded first ligand). According tocertain aspects of the invention, the excess, unreacted first ligand maybe removed by vacuum evaporation of the complex, and may include one ormore wash steps with an appropriate solvent, to yield a final dry powderhaving stoichiometric amounts of the metal, first ligand, and secondligand. For silver metal complexes, this powder is typically white.

The resulting purified metal complexes are substantially or totally freeof particles (particle-free) including nanoparticles and microparticles,and are highly soluble in various solvents. This differs greatly fromprior art complexes which do not include stoichiometric amounts of themetal, first ligand, and second ligand; and/or may include residualunliganded first ligand; and generally include particles such asnanoparticles and/or microparticles. Printing of these prior artnanoparticle inks on certain textiles has demonstrated that they oftendo not penetrate into the textile, but rather pool on top of thetextile, as observed in the scanning electron microscopy images shown inFIGS. 4A-4D, and the schematic in FIG. 4F, and thus do not formconductive traces (see FIG. 4E). The conductive inks of the presentinvention are capable of conformally coating fibers of a textilesubstrate (see FIG. 4G).

According to certain aspects of the present invention, the conductiveinks may be formulated by dissolving at least one purified metalcomplex, which is free of any unreacted first ligand, in an organicsolvent system such as a hydrocarbon solvent system.

According to certain aspects of the present invention, the conductiveinks may be formulated by dissolving at least one purified metalcomplex, which is free of any unreacted first ligand, in at least onepolar protic solvent, such as at least two polar protic solvents. Ingeneral, polar protic solvents can have high polarity and highdielectric constants. Polar protic solvents may comprise, for example,at least one hydrogen atom bound to an oxygen or a nitrogen. Polarprotic solvents may comprise, for example, at least one acidic hydrogen.Polar protic solvents may comprise, for example, at least one unsharedelectron pair. Polar protic solvents may display, for example, hydrogenbonding.

The viscosity of hydrogen bonding solvents is inherently greater thannon-hydrogen bonding solvents such as hydrocarbons. Further the elevatedsolvent boiling points (due to energetically greater intermolecularforces) and polar ink nature render them capable and competent systemsfor the formation of thin films and structures of greater quality thanstrictly hydrocarbon or aromatic hydrocarbon delivery systems due toslower controlled drying times, surface tensions, and surface wettingproperties.

Polar protic solvents may be particularly useful for depositing theconductive inks on certain substrates, since hydrocarbon solvent(s) maynot be compatible with the substrate and/or may not be recommended insome situations. Moreover, polar protic solvents may provide a moreenvironmentally friendly ink solution.

Examples of polar protic solvents include water, linear or branchedalcohols, amines, amino alcohols, and hydroxyl-terminated polyolsincluding glycols. The polar protic solvent may also be, for example,ethylene and higher glycols, as well as alcohols. Particular examples ofpolar protic solvents include water, methanol, ethanol, n-propanol,isopropanol, n-butanol, acetic acid, formic acid, and ammonia.

The polar protic solvent may include, for example, at least one aminesolvent. The amine solvent may have a molecular weight of, for example,about 200 g/mol or less, or about 100 g/mol or less. The amine solventmay be, for example, at least one monodentate amine, at least onebidentate amine, and/or at least one polydentate amine. The aminesolvent may be, for example, at least one primary amine or at least onesecondary amine. In one embodiment, the amine solvent may comprise atleast one alkyl group bonded to at least one primary or secondary amine.In one particular embodiment, the amine solvent may comprise at leasttwo primary or secondary amine groups connected by a linear or branchedalkyl group. In another particular embodiment, the amine solvent maycomprise at least two linear or branched alkyl groups connected by atleast one secondary amine. Advantages of the amine solvent include, forexample, improved solubility and thus higher possible concentrations ofthe metal complex in the solvent, as well as lower decompositiontemperatures for the metal complex.

The conductive inks of the present invention may be formulated toinclude hydrogels and/or polymers, such as polyacrylic acids, havinglower molecular weights, and which may function as viscosity modifiers.For example, the compositions may include up to 5 wt. % of a hydrogeland/or polymer, such as up to 4 wt. %, or up to 3 wt. %, or up to 2 wt.%, or up to 1 wt. %, or up to 0.5 wt. %, or up to 0.1 wt. %, or up to0.05 wt. %. The compositions may include hydrogels and/or polymers atfrom 0.01 wt. % to 5 wt. %, such as 0.01 wt. % to 4 wt. %, or 0.01 wt. %to 3 wt. %, or 0.01 wt. % to 2 wt. %, or 0.01 wt. % to 1 wt. %.According to certain aspects, the polymer may be a conductive polymer,such as any of the polyacetylenes, polyanilines, polyphenylenes,polypyrenes, polypyrroles, polythiophenes, etc. known in the art.

The metal complexes described herein may have a solubility in at leastone polar protic solvent at 25° C. of at least 50 mg/ml, or at least 100mg/ml, or at least 150 mg/ml, or at least 200 mg/ml, or at least 250mg/ml, or at least 300 mg/ml, or at least 400 mg/ml, or at least 500mg/ml, or at least 1,000 mg/ml, or at least 1,500 mg/ml, or even or atleast 2,000 mg/ml.

According to certain aspects, the amount of organic solvent in theconductive inks disclosed herein can be, for example, less than 30 wt.%, less than 20 wt. %, less than 10 wt. %, less than 5 wt. %, less than3 wt. %, less than 1 wt. %, less than 0.1 wt. % or less than 0.01 wt. %.According to certain aspects, the conductive ink formulations may besubstantially or totally free of organic solvent.

Analysis of the conductive ink formulations, in either of the organic orpolar protic solvent systems, has shown that the amounts of the metal,and first and second ligands, in the ink solutions are stoichiometric(see Examples).

According to certain aspects of the present invention, the viscosity ofthe ink formulations measured at 25° C. can be, for example, about 800cps or less, about 500 cps or less, about 250 cps or less, or about 100cps or less. According to certain other aspects, the viscosity of theink formulations measured at 25° C. can be, for example, about 50 cps orless, 40 cps or less, 30 cps or less, 25 cps or less, 20 cps or less, oreven 10 cps or less. According to yet other aspects, the inkformulations have a viscosity of about 1 cps to about 20 cps, or about 1cps to about 15 cps, or about 1 cps to about 10 cps.

According to certain aspects of the present invention, the viscosity ofthe ink formulations measured at 25° C. can be, for example, about 800cps or more, such as about 1500 cps or more, about 2,500 cps or more,about 5,000 cps or more, or even about 10,000 cps or more.

The conductive ink formulations may be substantially or totally free ofparticles, microparticles, and nanoparticles. In particular, theconductive ink formulations comprising the metal complex may besubstantially or totally free of nanoparticles including metalnanoparticles, or free of colloidal material. For example, the level ofnanoparticles can be less than 1 wt. %, less than 0.1 wt. %, or lessthan 0.01 wt. %, or less than 0.001 wt. %. One can examine thecomposition for particles using methods known in the art including, forexample, SEM and TEM, spectroscopy including UV-Vis, dynamic lightscattering, plasmon resonance, and the like. Nanoparticles can havediameters of, for example, 1 nm to 500 nm, or 1 nm to 100 nm.Microparticles can have diameters of, for example, 0.5 μm to 500 μm, or1 μm to 100 μm.

Metal Complex

The metal complex may comprise a metal useful for forming electricallyconducting lines, particularly those metals used in the semiconductorand electronics industries. Exemplary metals include at least silver,gold, copper, platinum, ruthenium, nickel, cobalt, palladium, zinc,iron, tin, indium, and alloys thereof. The metal complexes may comprisea single metal center or two metal centers.

For example, the metal complex may be a neutral metal complex comprisingat least one metal, at least one first ligand, and at least one secondligand. The first ligand may be adapted to volatilize when heatedwithout formation of a solid product. For example, the first ligand mayvolatize upon heating at a temperature of, for example, 250° C. or less,or 200° C. or less, or 150° C. or less. Heating can be done in thepresence or absence of oxygen. The first ligand may be a reductant forthe metal. The first ligand may be in neutral state, such as neither ananion nor a cation.

The first ligand may be a monodentate ligand, or a polydentate ligandincluding, for example, a bidentate or a tridentate ligand. According tocertain aspects of the invention, the first ligand may be a thioether,such as tetrahydrothiophene, a phosphine, or an amine compound. Incertain examples, the first ligand may comprise an amine compound havingat least two primary amine groups. Primary amines are stronger reducingagent than alcohols and are capable of forming homogenous solutions withpolar protic solvents. Moreover, the first ligand may comprise twoprimary amine end groups and no secondary amine group, or one primaryamine end group and one secondary amine end group. In this latterexample, the secondary amine end group may be substituted with a linearalkane or a polar group, such as a hydroxy or alkoxy. In yet anotherexample, the first ligand may comprise two primary amine end groups andone secondary amine group. The first ligand may be an amine including analkyl amine. The alkyl groups can be linear, branched, or cyclic.Bridging alkylene can be used to link multiple nitrogen together. In theamine, the number of carbon atoms can be, for example, 15 or less, or 10or less, or 5 or less.

The molecular weight of the first ligand, may be, for example, about1,000 g/mol or less, or about 500 g/mol or less, or about 250 g/mol orless.

In particular examples, the first ligand is ethylenediamine,1,3-diaminopropane, diaminocyclohexane, or diethyl ethylenediamine.

The second ligand is different from the first ligand and may alsovolatilize upon heating the metal complex. For example, the secondligand may release carbon dioxide, as well as volatile small organicmolecules. The second ligand may be adapted to volatilize when heatedwithout formation of a solid product. The second ligand may volatizeupon heating at a temperature of, for example, 250° C. or less, or 200°C. or less, or 150° C. or less. Heating can be done in the presence orabsence of oxygen. The second ligand can be anionic. The second ligandmay be self-reducing.

According to certain aspects of the invention, the second ligand may bea carboxylate. The carboxylate may comprise a linear, branched or cyclicalkyl group. In one embodiment, the second ligand does not comprise anaromatic group. The second ligand may be an amide represented by—N(H)—C(O)—R, wherein R is a linear, branched or cyclic alkyl group,with 10 or fewer carbon atoms, or 5 or fewer carbon atoms. The secondligand can also be an N-containing bidentate chelator.

The molecular weight of the second ligand, including the carboxylate,may be, for example, about 1,000 g/mol or less, or about 500 g/mol orless, or about 250 g/mol, or about 150 g/mol or less or less.

In particular examples, the second ligand may be isobutyrate, oxalate,malonate, fumerate, maleate, formate, glycolate, lactate, citrate, ortartrate.

Thus, according to certain aspects of the present invention, the metalcomplex may comprise at least one metal, at least one first ligand, andat least one second ligand, wherein the metal may be silver, gold, orcopper. Exemplary first ligands include amines and sulfur containingcompounds, and exemplary second ligands include carboxylic acids,dicarboxylic acids, and tricarboxylic acids. Exemplary solvents includeone or more polar protic solvents, such as at least two polar proticsolvents selected from the group comprising at least water, alcohols,amines, amino alcohols, polyols, and combinations thereof.

According to certain other aspects, the metal complex may comprise atleast one first metal complex having at least one first metal, at leastone second metal complex having at least one second metal, at least onethird metal complex having at least one third metal, and so forth,wherein each metal complex may comprise stoichiometric amounts of ametal and first and second ligands. For example, the metal complex maycomprise two neutral metal complexes formed as detailed above (i.e.,having stoichiometric amounts of at metal and first and second ligands).

According to certain other aspects of the present invention, the metalcomplex may be configured to provide a metal alloy (e.g., after curingin the textile substrate). The metal complex may comprise at least onefirst metal complex, wherein the first metal complex comprises a firstmetal and at least one first ligand and at least one second ligand,different from the first ligand; and at least one second metal complex,which is different from the first metal complex, and comprises a secondmetal and at least one first ligand and at least one second ligand,different from the first ligand, for the second metal; and at least onesolvent. The (i) the selection of the amount of the first metal complexand the amount of the second metal complex, (ii) the selection of thefirst ligands and the selection of the second ligands for the first andsecond metals, and (iii) the selection of the solvent may be adapted toprovide a homogeneous composition.

According to yet other aspects, the metal complex may comprise at leastone first metal complex having at least one first metal in an oxidationstate of (I) or (II), and at least two ligands, wherein at least onefirst ligand is an amine and at least one second ligand is a carboxylateanion; at least one second metal complex, which is different from thefirst metal complex, wherein the second metal complex is a neutralcomplex comprising at least one second metal in an oxidation state of(I) or (II), and at least two ligands, wherein at least one first ligandis a sulfur compound and at least one second ligand is the carboxylateanion of the first metal complex.

According to certain other aspects of the present invention, the metalcomplex may comprise at least one first metal complex, wherein the firstmetal complex is a neutral, dissymetrical complex comprising at leastone first metal in an oxidation state of (I) or (II), and at least twoligands, wherein at least one first ligand is an amine and at least onesecond ligand is a carboxylate anion; at least one second metal complex,which is different from the first metal complex, wherein the secondmetal complex is a neutral, dissymmetrical complex comprising at leastone second metal in an oxidation state of (I) or (II), and at least twoligands, wherein at least one first ligand is sulfur compound and atleast one second ligand is the carboxylate anion of the first metalcomplex; at least one organic solvent, and wherein the atomic percent ofthe first metal is about 20% to about 80% and the atomic percent of thesecond metal is about 20% to about 80% relative to the total metalcontent.

Exemplary metals for use in these metal alloys include Sc, Ti, V, Cr,Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, La, Hf,Ta, W, Re, Os, Ir, Pt, Au, and Hg. In particular, coinage metals can beused including silver, gold, and copper. Precious metals can be usedincluding gold, iridium, osmium, palladium, platinum, rhodium,ruthenium, and silver. In other preferred embodiments, platinum, nickel,cobalt, and palladium can be used. Still further, lead, iron, tin,ruthenium, rhodium, iridium, zinc, and aluminum can be used. Othermetals and elements can be used as known in the art.

According to certain aspects, the first metal complex is a silver, gold,copper, platinum, nickel, iridium, or rhodium complex. For example, thefirst metal complex may be a silver complex. According to certainaspects, the second metal complex is a silver, gold, copper, platinum,nickel, iridium, or rhodium complex. For example, the second metalcomplex may be a gold complex. Examples of binary combinations of metalsto form binary alloys include at least Ag—Au, Pt—Rh, Au—Cu, Zn—Cu,Pt—Cu, Ni—Al, Cu—Al, Pt—Ni, and Pt—Ir.

The metal complexes of the metal alloy can comprise a plurality ofligands including two or more ligands, or just two ligands. There canbe, for example, a first ligand and a second ligand, different from eachother. The first ligand can provide sigma electron donation, or dativebonding. The first ligand can be in a neutral state, not an anion orcation. Examples of the first ligand include amines, oxygen-containingligands, and sulfur-containing ligands including oxygenated ethers andthioethers, including cyclic thioethers. Asymmetrical or symmetricalamines can be used. The amines can comprise, for example, at least twoprimary or secondary amine groups. Monodentate ligands can be used.Polydentate or multidentate ligands can be used. Alkylamino ligands canbe used.

The second ligand can be different from the first ligand and canvolatilize upon heating the metal complex. For example, it can releasecarbon dioxide, as well as volatile small organic molecules such aspropene, in some embodiments. The second ligand can be a chelator withminimum number of atoms that can bear an anionic charge and provide aneutral complex. The second ligand can be anionic. For example, thesecond ligand can be a carboxylate, including a carboxylate comprising asmall alkyl group. The number of carbon atoms in the alkyl group can be,for example, ten or less, or eight or less, or five or less. Themolecular weight of the second ligand can be, for example, about 1,000g/mol or less, or about 250 g/mol or less, or about 150 g/mole or less.

The metal complexes of the presently disclosed invention can besubstantially or totally free of particles, including nanoparticles andmicroparticles, when in the dried state (powder) or when formulated asan ink in at least one solvent. The ink can be substantially or totallyfree of particles, including nanoparticles and microparticles, beforedeposition or printing. The ink can be substantially or totally free ofparticles, including nanoparticles and microparticles, after depositionbut before reduction to metal (e.g., before curing). The ink can besubstantially or totally free of particles, including nanoparticles andmicroparticles, after deposition and reduction to metal.

Direct Printing

Methods known in the art can be used to deposit inks including, forexample, pipetting, inkjet printing, lithography or offset printing,gravure or gravure offset printing, flexographic printing,microdispersion direct write printing, screen printing or rotary screenprocess printing, offset printing, stencil printing, drop casting, slotdie, roll-to-roll, stamping, roll coating, spray coating, flow coating,extrusion printing, and aerosol delivery such as spraying or pneumaticor ultrasonic aerosol jet printing. One can adapt the ink formulationand the substrate with the deposition method.

In certain examples, the inks are deposited by direct printing methodssuch as pipetting, stencil printing, rolling, spraying, or inkjetprinting. In certain example, the particle-free conductive inks aredeposited using inkjet printing.

According to certain aspects, the conductive inks of the presentinvention are printed directly onto a surface of the textile.

According to certain aspects, certain textile substrates may benefitfrom pre-treating the textile, such as prewashing the textile andoptionally treating by oxygen plasma, corona, and/or chemical etch(e.g., acidic, caustic). Accordingly, the conductive inks of the presentinvention may be printed on the textile substrate after it has beenpretreated by oxygen plasma, corona, and/or chemical etch.

According to certain other aspects of the present invention, certaintextile substrates may benefit from addition of a coating. For example,cellulose based substrates such as paper and/or cotton textiles may needa coating to reduce ink bleed and enhance conductivity of traces formedthereon. That is, the cellulose or cotton based substrates may be coatedwith a transparent layer, such as a polyurethane coating prior toprinting the conductive pattern.

One can adapt the viscosity of the ink to the deposition method. Forexample, viscosity can be adapted for inkjet printing. Viscosity of theink formulations measured at 25° C. can be, for example, about 500 cpsor less, such as 200 cps or less, or 50 cps or less, or even 25 cps orless. Viscosity of the ink formulations measured at 25° C. can be, forexample, at least 50 cps. Viscosity of the ink formulations measured at25° C. can be, for example, about 50 cps or less, such as about 25 cpsor less. According to certain other aspects, the viscosity of the inkformulations measured at 25° C. can be, for example, about 1 cps toabout 20 cps, or about 1 cps to about 10 cps. Viscosity of the inkformulations may be tuned through selective ratios of polar proticsolvents (e.g., ratio of water to amine).

Alternatively, the ink viscosity can be formulated, for example, to begreater than 15 cps, or 20 cps, or even 25 cps, such as by addition ofbinders, resins, or other additives or solids that may thicken orincrease the viscosity of the ink formulation. For example, one canadapt the concentration of dissolved solids in the ink to about 2,000mg/ml, or 1,500 mg/ml or less, about 1,000 mg/ml or less, about 500mg/mL or less, about 250 mg/mL or less, about 100 mg/mL or less, about50 mg/mL or less, or about 10 mg/mL or less.

Additives may also be included to adapt the wetting properties of theink. Additives such as, for example, surfactants, dispersants, colorant(e.g., dye), and/or binders can be used to control one or more inkproperties as desired. For example, a hydrophilic binder may aid inwetting certain textiles, and thus may aid in providing a conductivetrace that conformally coats the textile fibers (i.e., improveconductivity of the conductive trace). For example, the conductive inkformulations may include up to 10 wt. % of one or more additives, suchas up to 8 wt. %, or up to 6 wt. %, or up to 4 wt. %, or up to 2 wt. %,or up to 1 wt. %, or up to 0.1 wt. %, or up to 0.05 wt. %. Thecompositions may include additives at from 0.01 wt. % to 5 wt. %, suchas 0.01 wt. % to 4 wt. %, or 0.01 wt. % to 3 wt. %, or 0.01 wt. % to 2wt. %, or 0.01 wt. % to 1 wt. %.

According to certain aspects, the ink formulations of the presentinvention are substantially or totally free of additives such assurfactants, dispersants, colorant (e.g., dye), and/or binders.

Nozzles can be used to deposit the precursor, and the nozzle diametercan be, for example, less than 200 micrometers, or even less than 100micrometers. The absence of particulates can help with prevention ofnozzle clogging. The nozzle may deposit the ink in droplets, wherein adrop size may be less than 200 micrometers, such as less than 100micrometers, or less than 50 micrometers, or even less than 30micrometers. The nozzle may deposit the ink in droplets, wherein a dropvolume is less than 100 picoliter (pL), or less than 50 pL, or less than25 pL, or even less than 15 pL. The drops may be deposited at a densitygreater than 30 drops per inch, such as greater than 60 drops per inch,or greater than 90 drops per inch, or greater than 200 drops per inch,or greater than 500 drops per inch, or greater than 1,000 drops perinch, or greater than 1,500 drops per inch, or greater than 2,500 dropsper inch, or greater than 4,000 drops per inch, or greater than 6,000drops per inch.

According to certain aspects of the present invention, the particle-freeconductive inks of the present invention may be printed on textilesubstrates at ambient conditions, such as at standard room temperaturesand pressures.

According to certain aspects of the present invention, the textilesubstrate may be heated before and/or during deposition of the ink. Forexample, the textile substrate may be heated to temperatures of 40° C.to 90° C. With reference to FIG. 6 , an exemplary inkjet printer 10 isshown which includes a heated platen 12 and a nozzle assembly 14. Inuse, the particle-free conductive inks of the present invention may beloaded to the printer 10 so that droplets of the ink may be deposited.The platen 12 may be heated to temperatures of 30° C. to 90° C., such as30° C. to 60° C., or 40° C. to 90° C. during printing.

While specific numbers are listed herein for the size and density of thedroplets, volume of the droplets, and the nozzle size, these values mayvary depending on the printing method chosen, the printer chosen (e.g.,nozzle configuration), the viscosity of the conductive ink, and thecoverage desired.

Thus, according to certain methods of the present invention, theconductive inks of the present invention may be deposited on a substratesuch as a textile that is heated during deposition, followed by a curingstep that converts the metal complex in the ink formulation to ametallic structure (“in situ curing”). Thus, as used herein, in situcuring may be taken to mean heating the textile during deposition of theconductive ink followed by any of the curing steps detailed herein thatconvert the metal complex in the ink formulation to a metallicstructure.

According to certain other methods of the present invention, theconductive inks of the present invention may be deposited on a substratesuch as a textile at ambient temperatures (and pressures), followed by acuring step that converts the metal complex in the ink formulation to ametallic structure (“ex situ curing”). Thus, as used herein, ex situcuring may be taken to mean that the textile is not heated duringdeposition of the conductive ink, and before any of the curing stepsdetailed herein that convert the metal complex in the ink formulation toa metallic structure.

Shown in FIGA. 7A and 7B are the front and back, respectively, of anexemplary e-textile produced using methods and inks according to thepresent invention. For example, an exemplary silver ink formulation mayinclude a silver complex having stoichiometric amounts of first andsecond ligands, dissolved in two or more polar protic solvents, such aswater and any of an alcohol and/or amine. Generally, such an inksolution is formulated to include the silver complex at 250 mg/ml orgreater, such as 500 mg/ml. These solutions are clear. Heating thetextile during deposition of the conductive ink may reduce the ink bleedoutside of the printed region. For example, the conductive traces formedusing the inks and methods of the present invention may exhibit an inkbleed of less than 0.5 mm, such as less than 0.4 mm, or less than 0.3mm, or less than 0.2 mm, or even less than 0.1 mm. As used herein, theterm “ink bleed” may be taken to mean a measure of the precision of theink deposition and is referred to in terms of the distance from adefined edge (intended border) of a printed trace that the ink mayextend.

An exemplary solution of 500 mg/ml of an ink composition according toaspects of the present invention may have a viscosity of about 5-15 cpsat 25° C., a density of about 1.0-1.3 g/mL, a pH of at least 10-13, asurface tension of about 15-34 dyne/cm, and a silver content of about15-25 wt. %. Ink jet printing of such an ink may include depositing theink as droplets of between 5-200 micrometers at 60-6,000 drops per inchto a textile substrate heated at between 30° C. to 90° C. on the platen12, such as 65 micrometers at 1270 drops per inch. The textile may thenbe cured at a temperature of less than 200° C. for a time of less than30 minutes, such as for between 2-20 minutes at 140° C., or 10 minutesat 140° C. Alternatively, the textile may be cured by exposure toinfrared radiation for a time of less than 30 minutes, such as forbetween 2-20 minutes, or 10 minutes. An exemplary line wide resultingfrom this method may about 2 mm, and may show an ink bleed of less than0.5 mm, such as less than 0.2 mm, or even less than 0.1 mm. Moreover,the pattern demonstrated a resistivity of less than 10Ω/□, such as lessthan 5Ω/□, or less than 1Ω/□, or from 0.1Ω/□ to 0.9 Ω/□.

According to certain aspects, the conductive traces of the presentlydisclosed invention may have sheet resistance values of less than10.0Ω/□, or less than 8.0Ω/□, or less than 6.0Ω/□, or less than 4.0Ω/□,or less than 2.0Ω/□, or less than 1.0Ω/Ω, such as from 0.1Ω/□ to 1.0Ω/□.Certain applications of the conductive traces may benefit from increasedsheet resistance, such as more than 2.0Ω/□ or 10.0Ω/□, such as resistiveheaters.

Exemplary systems that may be used in methods of the presently disclosedinvention include FujiFilm Dimatix DMP 2850 and DMP 2931. Using thisprinter, the particle-free conductive inks of the present invention maybe printed to textiles pre-heated on the platen using a drop size of5-200 micrometers, or a drop volume of less than 100 pL, at 60-6,000drops per inch. The textile may then be cured on the platen in thedevice, such as for 10 minutes at 140° C. or 10 minutes exposure toinfrared radiation, or removed to an oven or other area for curing,wherein the metal in the metal complex turns to a solid conductivemetal. Curing may be by any method disclosed herein.

Key factors affecting the conductivity achievable by the presentlydisclosed inks and printing methods include compatibility of the inkchemistry with the surface energy of the textile, the textile size andstructure (woven, non-woven), pretreatment of the textile, such as withO₂ plasma, and the curing methods, such as the in situ heating of thetextile during printing which provides high resolution traces, and thelow temperature curing (<200° C.; see section below regarding curing).Thus, the presently disclosed inks and methods provide a large advantageover the prior art inks shown in FIGS. 4A-4E, wherein the particles ofthe ink may clog the nozzles of an inkjet device, and traces formedusing the inks are generally non-conductive (i.e., show very high sheetresistance) and non-compatible with many textiles as they require highcure temperatures.

An exemplary textile printed as detailed above is shown in FIGS. 7A-7Band 8A-8C. Shown in FIGS. 7A-7B, are front (top) and back (bottom) sidesof a nonwoven textile substrate printed with the particle-freeconductive inks of the present invention and cured to form theconductive pattern (i.e., converted to a metallic structure) using insitu curing.

Shown in FIG. 8A is a close-up view of a woven textile substrate havingprinted section (left) and a non-printed section (right), whereinprinting was on a heated substrate (in situ heat cure) using theparticle-free conductive inks of the present invention. FIGS. 8B and 8Cshow scanning electron microscopy images (SEM) of the printed textiletaken by SEM (150× and 800× magnification). These images demonstratethat the in situ curing demonstrates better “dying” of the fibers of thesubstrate. That is, the particle-free inks according to the presentinvention may better penetrate (e.g., soak into the fibers of thetextile), or may more completely coat an outer surface (e.g.,encapsulate or soak into an outer surface of the textile; conformalcoating) of a heated textile substrate, acting as a dye on the textilesubstrate and improving the conductivity of patterns formed in theheated substrates. Prior art conductive inks, which comprise particles(nanoparticles, flakes, etc.), would not be able to penetrate thetextile and were found to sit on top of the textile substrate as shownin FIGS. 4A and 4B. This leaves the prior art inks more susceptible toremoval by abrasion and other forces exerted on the textile substratethrough standard wear and tear. Thus, the in situ heat curing promotesbetter coating around the fabric thread (i.e., conformal coating; seeFIG. 4G).

The present inventors have found that the sheet resistance values fortextiles (knit, woven, and nonwoven such as Evolon®) printed with theparticle-free conductive inks according to the present invention usingin situ curing is improved over ex situ curing for most textilesubstrates. The in situ curing lowers the sheet resistance, in somecases several orders of magnitude over values measured from ex situcured conductive traces, and also reduces the ink bleed. These resultswere consistent for all numbers of printed layers tested (number oflayers in the conductive trace). Thus, methods of the presentlydisclosed invention, which include heating of the textile duringdeposition of the ink, such as by ink jet printing, not only leads toimproved trace resolution, but also improved conductivity of the trace.

Additionally, the sheet resistance values for knit and non-woven(Evolon®) textiles printed with the particle-free conductive inksaccording to the present invention were improved by pretreatment byoxygen plasma or corona. Accordingly, methods of the presently disclosedinvention, which include heating of the textile before and/or duringdeposition of the ink, such as by ink jet printing, may also includepretreatment of the textile, and may provide improved conductivity ofthe trace over untreated textiles.

Textile Substrates

A wide variety of solid materials can be subjected to deposition (e.g.,printing) of the particle-free conductive inks of the present invention.Polymers, organic and synthetic fibers, plastics, metals, ceramics,glasses, silicon, semiconductors, and other solids can be used. Organicand inorganic substrates can be used.

In particular examples, the substrate is a textile such as a knit,woven, or nonwoven fabric formed of organic or synthetic fibers.Exemplary fibers of such textile substrates include at least polyester,polyamides, spandex, polyester-spandex, nylon, nylon-spandex, Evolon®,elastane, and other synthetic materials, in addition to organicmaterials (e.g., cotton, cellulose, silk, wood, wool fibers, leather,suede). Blends of any of these materials are also possible.

According to certain aspects of the invention, the textiles may bepretreated with a reactive gas, such as an O₂ plasma or corona, that mayimprove deposition of the particle-free conductive inks thereon, and mayreduce sheet resistance.

Additionally, the textiles may be prewashed and dried prior todeposition or printing of the conductive inks disclosed herein.

Curing the Particle-Free Conductive Inks

Once the particle-free conductive ink formulations have been printedonto a substrate, such as a textile substrate, at either ambienttemperatures or elevated temperatures, they may be cured to form theconductive pattern (i.e., converted to a metallic structure). Curing caninclude heating the printed substrate, and/or irradiating the printedsubstrate. In certain examples, the printed substrate may be cured byheating to a temperature of 200° C. or less, such as 150° C. or less, or100° C. or less, for a time period of less than 60 minutes, such as lessthan 30 minutes, or less than 15 minutes. In a particular example, theprinted substrate is heated to 140° C. for 10 minutes, or exposed toinfrared radiation for 10 minutes, to form a conductive pattern with aresistance of less than 1 Ω/□.

Exemplary sheet resistance values are shown for knit, woven, andnonwoven textiles cured ex situ or in situ (i.e., printed on the textileat ambient temperatures and cured; or printed on the textile at elevatedtemperatures and cured; FIG. 10 ). The lowest sheet resistance was foundfor conductive traces on woven polyester, with either in situ or ex situcuring, while both the knit and nonwoven textiles benefited from in situcuring. Close-up views of the coated fibers of knit, nonwoven, and woventextiles cured either ex situ or in situ are also shown in FIGS. 7A-7F.

In certain examples, the conductive trace on the textile substrate maybe additionally, or alternatively, cured by exposure to pulsed light,such as by photonic curing, wherein the number of pulses ranges from 2to 20. Alternatively, or in addition, curing may include irradiating theconductive trace on the textile substrate, such as by exposure toinfrared radiation.

Protective Coatings

According to certain aspects of the present invention, the conductivetraces formed using the particle-free inks disclosed herein may becoated with a protective coating, such as a dielectric coating. Forexample, all or a portion of a trace may be coated with a polymercoating, such as an aqueous dielectric polymer solution. Exemplarypolymer solutions include at least acrylic and polyurethane polymers.The protective coating can be deposited by painting, spraying, orprinting (e.g., inkjet printing). The viscosity of the polymericsolutions can be adjusted for the specific textile and deposition methodby dilution with appropriate solvents and solvent mixtures. Suchcoatings may be cured by heat treatment, evaporation of solvents,irradiation (e.g., UV treatment), or any combination thereof. Anexemplary coating includes an acrylic-based coating that is printed overthe conductive trace and is cured by heating the textile to 160° C. orless, such as 150° C. or less for 30 minutes or less, such as 20 minutesor less.

The coatings may improve washability of the conductive traces, as shownin FIG. 11 , and may also improve abrasion resistance of the conductivetraces (see Table 5 in examples).

Additional coatings may be provided over contact regions, such as at thecontact points or pads of a trace. Such coatings may include conductivepolymers and may provide conductive contact with the printed trace whilealso protecting the trace from abrasion and/or during wash cycles.

E-Textile

The present invention is also directed to e-textiles. These e-textilesinclude any textile having printed thereon at least one conductive traceor pattern using inks and/or methods disclosed herein. The traces mayterminate in contact pads or connectors for connection to a current,such as a power supply or battery. Various hardware elements may beconnected to portions of the trace or pattern to form electric devices.As such, the conductive patterns on the e-textiles may be formed as atrace or pattern that may provide a sensor (e.g., optical, thermal,humidity, gas, pressure, acceleration, strain, force, and proximity), aconductor, an electrode, a circuit, an interconnect, a light, anantenna, a resistive heating element, a switch, a transparent conductiveelement, a battery, or any combination thereof. An exemplary e-textilecomprising a proximity sensor according to the presently disclosedinvention is shown in FIG. 14 .

The e-textiles may be incorporated into or may be wearable electronicdevices. The e-textiles may find use in many different industries for awide range of uses, such as in the medical industry for healthmonitoring or as anti-microbial dressings, and in industrial settings assmart clothing or devices for gas sensing or filtration. The e-textilesmay find use in smart garments, such as for fitness monitoring, hygieneimprovement, or as flexible energy storage devices (e.g., batteries,supercapacitors). The e-textiles may find use as resistive heaters, suchas in a wearable garment or in an automobile (e.g., seat heater,electric vehicle heater). An exemplary 5-trace heating element accordingto the presently disclosed invention is shown in FIG. 7A.

Exemplary e-textiles may include, for example, a directional compass,one or more gyroscopes, one or more accelerometers, pressure gauges,strain gauges, temperature gauges, and fiber optics. The sensorsemployed in e-textiles may be used to monitor parameters of a userwearing the e-textile, such parameters may include heart rate,respiration rate, skin temperature, and body position and movement.Moreover, e-textiles may be used to measure a user's full-bodybiomechanics such as joint angles, angular velocity, angularacceleration, and range of motion.

These e-textiles are found to have greatly improved wear performance,e.g., bendability, washability, strain resistance, etc., over e-textilesformed using the inks and methods of the prior art. For example, theconductive patterns on the fabric substrate may withstand at least 50wash cycles, such as at least 70 wash cycles, or even 100 wash cycleswith air drying (see FIG. 11 and examples). For example, the resistanceof the conductive traces formed using the inks and methods of thepresent invention may increase only slightly after multiple wash cycles,such as by less than 50% after 50 washes, or less than 30% after 50washes, or less than 15% after 50 washes, or less than 70% after 100washes, or less than 60% after 100 washes, or less than 40% after 100washes, or less than 30% after 100 washes, or less than 20% after 100washes, wherein a wash cycle is defined as in according to AATCC 61-2013(laundering). As shown in FIG. 11 , the protective coating may improvethe washability of the e-textiles disclosed herein.

The e-textiles may be abrasion resistant (up to 500 cycles by standardASTM testing methods), and may be sweat resistant (moisture resistant).

The e-textiles may be strain resistant. For example, knit e-textiles maybe stretched by up to 50%, or up to 100%, without connection loss,generally showing a small increase in conductivity with an increase instretching of the textile substrate (see FIG. 12 and examples).

The e-textiles may be bendable, showing less than a 10% loss inconductivity after up to 10,000 bend cycles using standard ASTM testingmethods (see FIG. 13 ).

E-Textile Resistive Heaters

According to certain aspects of the present invention, the conductiveinks may be used to print resistive heating elements on a textile. Suchelements may find application as wearable heaters or heating elementsfor use in clothing, or resistive heating elements in the automotiveindustry (e.g., seat heaters, electric car heaters) and others. Anexemplary 5-trace heater is shown in FIG. 15 . These heaters may beplaced in series, or parallel, as shown in FIGS. 17A and 17B,respectively.

Resistance measurements were taken at various points along the traces,as shown by the numbered blocks in FIG. 15 , and found to vary linearlywith respect to trace length (see FIG. 16A for values measure from two5-trace heaters). In fact, the calculated and measured resistance valuesat each point were found to be very close (i.e., resistance measuredwith an alligator clip ground connection and manual tip probe; see FIG.16B). Similar results were observed for 7-trace heaters. Left-to-rightand right-to-left resistance measurements were conducted to investigateprint/process-related resistance variations. When normalized for tracelength, the measured resistance from 5-trace and 7-trace heaters showedremarkable correlation with the predicted resistance.

An advantage of these resistive heaters is that they are flexible, thin,and heat/cool rapidly. For example, a 5-trace heater printed using theconductive inks and methods of the present invention can heat at a rateof about 0.7° C./second to about 1° C./second. Heating is initiatedalmost immediately after current is provided to the resistive heater.The upper temperature limit may be limited based on the total voltagesupplied to the printed trace, wherein an upper set point was found tohave little effect on the heating rate (i.e., heating to 65° C. and 85°C. occurs at the same rate).

The temperature increases linearly with power until an equilibrium isreached (see FIG. 18A, about 2 watts of power and 100° F.). Moreover,the resistance is not observed to drift with time (FIG. 18B) ortemperature (FIG. 18C) for resistive heaters printed using the inks andmethods of the presently disclosed invention. Such results are observeduniformly from trace to trace, showing an overall deviation of only 3Ω.

According to certain aspects of the present invention, the resistiveheaters may be configured to carry a power density of less than 400watts/m², such as less than 300 watts/m². According to other aspects,the resistive heaters of the present invention may not be capable ofcarrying a power density of 400 watts/m², and may only be capable ofcarrying a power density of less than 400 watts/m², such as less than350 watts/m², or less than 300 watts/m², or less than 200 watts/m², oreven less than 100 watts/m².

A thermal output from the resistive heaters will depend on variousdesign factors, such as the metal or alloy in the conductive ink, awidth of the conductive trace, a thickness of the conductive trace, theresistance of the trace, and any other components in the ink composition(e.g., other conductive polymers, etc.), and thus may be tuned to fitthe specific application.

Thus, according to certain aspects of the present invention, theresistive heaters may be configured to carry a power density of greaterthan 400 watts/m². For example, the resistive heaters of the presentinvention may be capable of carrying a power density of at least 600watts/m², such as at least 800 watts/m², or at least 1,000 watts/m², orat least 1,500 watts/m².

While specific embodiments of the invention have been described indetail, it should be appreciated by those skilled in the art thatvarious modifications and alternations and applications could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements, systems, apparatuses, andmethods disclosed are meant to be illustrative only and not limiting asto the scope of the invention.

Examples

Production of a Particle-Free Conductive Ink

Exemplary conductive inks comprising silver complexes comprising acarboxylate second ligand (e.g., silver carboxylate) may be formed byreaction of a metal oxide or metal-acetate and a carboxylic acid in areaction that affords analytically pure compounds and proceeds inquantitative yields.

As example, silver acetate was reacted with a carboxylic acid(isobutyrate and cyclopropate). The elemental analysis of the two silvercomplexes were C, 24.59; H, 3.72 and C, 24.68; H, 2.56 for theisobutyrate and cyclopropate, respectively. Theoretical values are C,24.64; H, 3.62 and C, 24.90; H, 2.61 for the isobutyrate andcyclopropate, respectively.

The metal-second ligand salt was then reacted with an excess of thefirst ligand to form the metal complex. In a typical preparation, silverisobutyrate was prepared as described above, and placed in a 25 mLone-neck 14/20 round bottom flask containing a Teflon coated magneticstir bar. To this was added 13 eq. ethylenediamine (amounts as shown inTable 1 below). The reaction proceeded for 2 h at room temperature withstirring, filtered to remove any particulates, and the unreactedethylenediamine was removed by rotary evaporation at 40° C. to yield awhite powder. Additional wash steps can be included. The isolated metalcomplex—ethylenediamine silver isobutyrate—was then dissolved to atleast 100 mg/ml in a mixture of polar protic solvents (water, propyleneglycol, and isopropanol) to form a particle-free conductive ink which isclear (see top right of FIG. 9 , and Table 2 below).

TABLE 1 Diamine Amount Silver (I) Carboxylate Amount (ethylenediamine)(silver isobutyrate) Yield 184 g, 46 g, 59 g 3059 mmol, 235 mmol, (99%)13 equiv. 1 equiv.

TABLE 2 Isolated Metal Complex Water Propylene glycol Isopropanol 2.20 g(30%) 3.08 g 0.77 g (11%) 1.25 g (17%) (42%)

Purity of the Metal Complex

Preparation of the metal complexes was found to require an excess of thefirst ligand reactant with the metal-second ligand (see table above;13-fold excess second ligand used to produce the metal complex). Asexample, most silver (I) carboxylates are insoluble in most conventionalsolvents. A 1:1 reaction (1:1 silver isobutyrate:ethylenediamine) gave adark colored product with a large amount of insoluble material,presumably unreacted silver (I) isobutyrate, when formulated in a polarprotic solvent system. Thus, the metal complexes formed by the 1:1reaction likely failed to promote complete conversion of all reactantsto products, and failed to form continuous conductive films on asubstrate.

A 1:6 reaction (1:6 silver isobutyrate:ethylenediamine), on the otherhand, formed crystals spontaneously from a filtered solution of thereaction. Moreover, while the metal complex did dissolve in the polarprotic solvent system, the presence of excess unreacted diamine wasfound to have a significant impact on the density, viscosity, andsurface tension of the ink formulations. The 1:6 product formulated asan ink shows poor sheet coverage and extremely high sheet resistance(>600,000Ω/□).

The 1:13 reaction product listed in the table above, which was purifiedto remove excess unreacted amine (first ligand) showed excellent sheetcoverage, and demonstrated a sheet resistance of less than 1Ω/□. Thepurified product, dissolved in a polar protic solvent system as shown inthe table above, showed a density of 1.12 g/mL, a viscosity of 8.55 cps,and a surface tension of 22.9 dyne/cm.

Accordingly, an important step in producing the particle-free conductiveinks of the present invention is removal of any unreacted second ligand,especially in view of the large excess used to formulate the final metalcomplex. When purified as detailed above, the product (yield 99%) iscolorless. Unpurified products, however, tend to be dark colored, whichis likely associated with normal darkening of diamines when exposed toopen air. In general, amines absorb moisture and carbon dioxideresulting in formation of unstable carbamates. Such speciation of aminesmay destabilize diaminosilver (I) carboxylates, which often results inpremature silver metallization, dark coloration and particle formation.Hence, removal of any residual amines is important to promote stabilityof diaminosilver (I) carboxylates, especially if concomitant preparationof zero-particulate diaminosilver (I) carboxylate compositions isrequired.

Stoichiometric Ratio of Ligands and Metal in the Metal Complex

The metal complex was found to comprise stoichiometric amounts of thefirst and second ligands and the metal. Structural analysis using protonNMR showed that the ethylenediamine silver isobutyrate powder dissolvedin D₂O consists of stoichiometric amounts of the ethylenediamine ligandcoordinated to silver isobutyrate. A ¹H-NMR spectrum of the metalcomplex in D₂O (see FIG. 9 ; ¹H-NMR scan on a Bruker AV-360spectrometer) showed the expected three proton-carbon (CH) peaks: 1 forthe two ethylenediamine CH₂ groups (4 protons total), 1 for the singleisobutyrate CH group (1 proton), and 1 for the two isobutyrate CH₃groups (6 protons total). These were assigned as: 0.93 ppm isobutyrateCH₃, 2.25 ppm isobutyrate CH, and 2.81 ppm ethylenediamine CH₂. Theproton integral ratio of 3.978 ethylenediamine CH₂: 0.928 isobutyrateCH:6.151 isobutyrate CH₃ is consistent with 1 ethylenediamine:1 silverisobutyrate, or stoichiometric amounts of the metal, and each of theethylenediamine and isobutyrate ligands.

In order to verify that the metal complex, when dissolved in two or morepolar protic solvents to form the ink, maintains a stoichiometric ratioof the first and second ligands and the metal, further ¹H-NMRexperiments were performed for the metal complex dissolved in a mixtureof three polar protic solvents as listed above (water, propylene glycol,isopropanol), and D₂O. The spectra in FIG. 10 shows well-resolved peaksfor the various polar protic solvents as well as the metal complex(ethylenediamine silver (I) isobutyrate), which are assigned as: 0.93ppm (doublet, isobutyrate CH₃), 2.25 ppm (septet, isobutyrate CH), and2.81 ppm (singlet, ethylenediamine CH₂).

The strong similarity between the chemical shifts of the metal complexin the NMR solvent (FIG. 9 ) and in the composition comprising the metalcomplex and two or more polar protic solvents (FIG. 10 ) suggestsexcellent compatibility between the metal complex and the polar proticsolvent system. The ethylenediamine silver (I) isobutyrate proton ratiosof 4.098 ethylenediamine CH₂:0.944 isobutyrate CH:6.446 isobutyrate CH₃are in good agreement with theoretical ratios of 4 ethylenediamine CH₂:1isobutyrate CH:6 isobutyrate CH₃; which demonstrates that dissolving themetal complex in a polar protic solvent carrier does not impact thecoordination environment around the metal (i.e., silver). This resultfurther corroborates the fact that the chemical composition of the metalcomplex remains unchanged when dissolved to form the ink composition(i.e., stoichiometry remains unchanged).

Formulation of Particle-Free Conductive Inks

Various polar protic solvents systems were tested to demonstrate theflexibility of the solvent choice for formulation of the particle-freeconductive inks of the present invention (see Tables 3 and 4 below). Forexample, a diamine silver (I) isobutyrate complex was formulated insolvent systems comprising at least two polar protic solvents.Representative ink formulations using different combinations of polarprotic solvents, and data showing that the ink formulations producecontinuous, highly conductive films (sheet resistance of 0.04-0.09Ω/□)when formulated in the polar protic solvents are shown in Tables 3 and 4below.

TABLE 3 Metal Complex Formulated in Polar Protic Solvent Systems GlycolGlycol metal ethylene propylene ether Alcohol composition complex waterglycol glycol (dowanol) ethanol isopropanol A 2.20 g 3.08 g — 0.77 g — —1.25 g B 2.01 g — — 0.77 g — — 4.25 g C 2.03 g 4.27 g — 0.78 g — — — D2.03 g 4.26 g 0.75 g — — — — E 2.00 g 3.00 g — 0.27 g — — 1.75 g F 2.01g 3.07 g — 0.13 g — — 1.91 g G 2.00 g 3.06 g —  1.5 g — — 0.51 g H 2.00g 3.02 g 0.75 g — — — 1.26 g I 2.02 g 3.03 g — 0.76 g — 1.26 g — J 2.04g 3.03 g — 0.76 g 1.26 g — — K 2.09 g 3.01 g — 0.51 g 0.76 g 0.76 g

TABLE 4 Density Viscosity Surface Tension Sheet Resistance composition(g/mL) (cP) (dyne/cm) (Ω/□) A 1.12 8.55 22.9 0.05 B 0.937 10.8 23.3 0.04C 1.15 4.60 25.3 0.08 D 1.15 3.77 24.7 0.08-0.09 E 1.09 6.99 23.6 0.06 F1.08 6.71 22.7 0.06 G 1.14 8.83 23.3 0.05 H 1.11 7.02 23.5 0.08 I 1.1121.3 23.8 0.06 J 1.14 8.25 23.5 0.9-01  K 1.12 8.21 22.7  005-0.06

Washability of Particle-Free Conductive Inks

The particle-free conductive inks of the presently disclosed inventionwere printed on various textiles to form conductive traces using ink jetprinting methods as disclosed hereinabove. The trace remained uncoated,or was coated with a transparent UV curable polyurethane coating. Sheetresistance for these patterns was tested according to AATCC 61-2013(laundering). As shown in FIG. 11 , very little change in theconductivity for the traces was observed after up to 50 washes. Thecoated trace shows good conductivity after as many as 100 wash cycles,while the native (uncoated) traces showed good conductivity after asmany as 70 wash cycles. The control samples completely lost conductivityafter only 5 wash cycles.

Analysis of various textiles according to AATCC 61-2013 demonstratedthat a conductive trace comprising 8 layers of printed ink showed lessthan a 3Ω increase in resistance after 100 wash cycles. When an abrasionresistant coating was included over the trace, the resistance onlyincreased by less than 0.7Ω.

Strain Resistance

Woven fabrics were printed using inks and methods according to thepresently disclosed invention, and subjected to strain resistancemeasurements. Shown in FIG. 12 are results for electromechanical stretchtesting under various amounts of stretching (0% to 230%). For conductivetraces of the prior art, strain induces film cracking which reducesconductivity (see FIG. 5 ). Using inks and methods according to thepresent invention, the trace conductivity was little affected by theincreased strain until the breakpoint of the textile (i.e., textile ripsinto two pieces). This unusual behavior is demonstrated by a very slightincrease in the average spot temperature of the trace (as measured usingFLIR; data not shown), where the spot temperature correlates to theamount of heat generated when electrons flow through a stretchedconductive fabric; the higher the temperature, the more heated generatedby the flowing electrons.

Bendability of the printed traces was also tested, as shown in FIG. 13 ,and only a small loss of conductivity (<10%) was observed for bending ofa conductive trace printed on woven textiles using inks and methods ofthe present invention (10,000× bends in the trace; tested according toASTM D522—Mandel Bend Test). Nonwoven textiles showed reducedperformance after 1,300 bends, which is likely a function of breakdownof the textile and not the conductive trace.

Abrasion Resistance

A woven substrate was printed with a conductive ink according to thepresent invention, and coated with an ablation resistance coating(Ablative Resistant Coating NSN 8030-00-164-4389) or left uncoated.Sheet resistance was measured for several textile samples after coating(control), 10×, 20×, and 30× rubbing (see Table 5).

TABLE 5 Resistance Q Before After After After After Sample coatingcoating rubbing 10X rubbing 20X rubbing 30X Uncoated 6-8 — 62-101132-138 300-382 Coated 6-8 6-7 9-10 11-12 12-13

The following aspects are disclosed in this application:

-   -   Aspect 1: A method for forming an e-textile, the method        comprising: depositing a particle-free conductive ink on a        textile substrate to form at least one pattern, wherein the        particle-free conductive ink conformally coats fibers of the        textile; and curing the particle-free conductive ink in the at        least one pattern to form at least one conductive pattern,        wherein the at least one conductive pattern exhibits an ink        bleed of less than 0.5 mm, and a resistance of less than 10 Ω/□.    -   Aspect 2: The method according to Aspect 1, wherein depositing        the particle-free conductive ink is by inkjet printing on the        textile substrate that is heated to a temperature of about        30° C. to about 90° C., such as about 40° C. to about 80° C.    -   Aspect 3: The method according to Aspect 2, wherein depositing        the particle-free conductive ink by inkjet printing comprises        printing two or more layers.    -   Aspect 4: The method according to any one of Aspects 1 to 3,        further comprising, during depositing the particle-free        conductive ink: heating the textile substrate to a temperature        of about 30° C. to about 90° C., such as about 40° C. to about        80° C.    -   Aspect 5: The method according to any one of Aspects 1 to 4,        wherein the at least one conductive pattern exhibits an ink        bleed of less than 0.2 mm.    -   Aspect 6: The method according to any one of Aspects 1 to 5,        wherein the at least one conductive pattern exhibits a        resistance of less than 5Ω/□, such as less than 1 Ω/□.    -   Aspect 7: The method according to any one of Aspects 1 to 6,        further comprising, after curing the particle-free conductive        ink: coating at least a portion of the conductive pattern with a        protective dielectric coating.    -   Aspect 8: The method according to any one of Aspects 1 to 7,        wherein the curing is by heating at a temperature of less than        200° C. for a time of less than 20 minutes, exposure to 2-20        pulses of pulsed light, exposure to infrared radiation, or any        combination thereof    -   Aspect 9: The method according to any one of Aspects 1 to 8,        wherein the textile substrate is pretreated with oxygen plasma,        a protective coating, or both.    -   Aspect 10: The method according to any one of Aspects 1 to 9,        wherein the particle-free conductive ink comprises: at least one        metal complex comprising: at least one metal, at least one first        ligand which is a sigma donor to the metal and volatilizes upon        heating the metal complex, and at least one second ligand, which        is different from the first ligand and also volatilizes upon        heating the metal complex; and one or more polar protic        solvents, wherein the metal complex has a solubility measured at        25° C. of at least 250 mg/ml in the one or more polar protic        solvents, and wherein the at least one metal, the at least one        first ligand, and the at least one second ligand are provided in        stoichiometric amounts in the conductive ink.    -   Aspect 11: The method according to Aspect 10, wherein the one or        more polar protic solvents comprise one or more of water, an        alcohol, and an amine.    -   Aspect 12: The method according to Aspects 10 or 11, wherein the        metal complex has a solubility measured at 25° C. of at least        500 mg/ml in the one or more polar protic solvents.    -   Aspect 13: The method according to any one of Aspects 1 to 12,        wherein the particle-free conductive ink comprises from 0.1% to        5% of an additive selected from one or more of a binder, a        surfactant, a dispersant, and a dye.    -   Aspect 14: The method according to any one of Aspects 1 to 13,        wherein the particle-free conductive ink has a viscosity        measured at 25° C. of 25 cps or less, such as 20 cps or less.    -   Aspect 15: The method according to any one of Aspects 1 to 14,        wherein the textile comprises a knit, woven, or nonwoven fabric        comprising fibers of polyester, polyamides, spandex, nylon,        Evolon®, elastane, cotton, cellulose, silk, wood, wool, or        blends thereof.    -   Aspect 16: An e-textile produced by any one of the methods of        Aspects 1-15, wherein the e-textile functions as a sensor, an        electrode, a circuit, an interconnect, a light, an antenna, a        resistive heating element, a switch, a battery, or any        combination thereof    -   Aspect 17: An e-textile comprising: a textile having at least        one particle-free conductive trace printed thereon, wherein at        least a portion of the at least one particle-free conductive        trace is over-coated with a protective dielectric coating,        wherein the at least one particle-free conductive trace exhibits        an ink bleed of less than 0.5 mm, and a resistance of less than        10 Ω/□.    -   Aspect 18: The method according to Aspect 17, wherein the at        least one conductive trace exhibits an ink bleed of less than        0.2 mm.    -   Aspect 19: The method according to any one of Aspects 17 or 18,        wherein the at least one conductive trace exhibits a resistance        of less than 5Ω/□, such as less than 1 Ω/□.    -   Aspect 20: The e-textile according to any one of Aspects 17 to        19, wherein the particle-free conductive trace comprises two or        more layers of a particle-free conductive ink.    -   Aspect 21: The e-textile according to any one of Aspects 17 to        20, wherein the textile comprises cellulose or cotton-based        fibers, and the textile is pretreated with a protective coating.    -   Aspect 22: The e-textile according to any one of Aspects 17-21,        wherein the resistance in the conductive trace is increased by        less than 50% after the textile is exposed to 50 wash cycles,        such as less than 50% after 100 washed, or less than 30% after        100 washes.    -   Aspect 23: The e-textile according to any one of Aspects 17-22,        wherein the textile comprises a knit, woven, or nonwoven fabric        comprising fibers of polyester, polyamides, spandex, nylon,        Evolon®, elastane, cotton, cellulose, silk, wood, wool, or        blends thereof.    -   Aspect 24: A resistive heater comprising: a textile having at        least one particle-free conductive pattern printed thereon,        wherein at least a portion of the particle-free conductive        pattern is over-coated with a protective dielectric coating,        wherein the resistive heater heats at a rate of about 0.7°        C./second to about 1° C./second, and wherein resistance in the        conductive trace is increased by less than 50% after the textile        is exposed to 50 wash cycles.    -   Aspect 25: The resistive heater of Aspect 24, wherein the        textile comprises a knit, woven, or nonwoven fabric comprising        fibers of polyester, polyamides, spandex, nylon, Evolon®,        elastane, cotton, cellulose, silk, wood, wool, or blends        thereof.

What is claimed is:
 1. A method for forming an e-textile, the methodcomprising: depositing a particle-free conductive ink on a textilesubstrate to form at least one pattern, wherein the particle-freeconductive ink conformally coats fibers of the textile; and curing theparticle-free conductive ink in the at least one pattern to form atleast one conductive pattern, wherein the at least one conductivepattern exhibits an ink bleed of less than 0.5 mm, and a resistance ofless than 10 Ω/□.
 2. The method of claim 1, wherein the conductivepattern exhibits an ink bleed of less than and a resistance of less than1 Ω/□.
 3. The method of claim 1, wherein depositing the particle-freeconductive ink is by inkjet printing on the textile substrate that isheated to a temperature of about 30° C. to about such as about 40° C. toabout 80° C.
 4. The method of claim 2, wherein depositing theparticle-free conductive ink by inkjet printing comprises printing twoor more layers.
 5. The method of claim 1, further comprising, duringdepositing the particle-free conductive ink: heating the textilesubstrate to a temperature of about 30° C. to about 90° C., such asabout 40° C. to about 80° C.
 6. The method of claim 5, wherein the atleast one conductive pattern exhibits an ink bleed of less than 0.2 mm.7. The method of claim 1, further comprising, after curing theparticle-free conductive ink: coating at least a portion of theconductive pattern with a protective dielectric coating.
 8. The methodof claim 1, wherein the curing is by heating at a temperature of lessthan 200° C. for a time of less than 20 minutes, exposure to 2-20 pulsesof pulsed light, exposure to infrared radiation, or any combinationthereof.
 9. The method of claim 1, wherein the textile substrate ispretreated with oxygen plasma, corona, a protective coating, or acombination thereof.
 10. The method of claim 1, wherein theparticle-free conductive ink comprises: at least one metal complexcomprising: at least one metal, at least one first ligand which is asigma donor to the metal and volatilizes upon heating the metal complex,and at least one second ligand, which is different from the first ligandand also volatilizes upon heating the metal complex; and one or morepolar protic solvents, wherein the metal complex has a solubilitymeasured at 25° C. of at least 250 mg/ml in the one or more polar proticsolvents, and wherein the at least one metal, the at least one firstligand, and the at least one second ligand are provided instoichiometric amounts in the conductive ink.
 11. The method of claim10, wherein the one or more polar protic solvents comprise one or moreof water, an alcohol, an amine, an amino alcohol, and a polyol.
 12. Themethod of claim 10, wherein the particle-free conductive ink comprisesfrom 0.1% to 5% of an additive selected from one or more of a binder, asurfactant, a dispersant, and a dye.
 13. The method of claim 10, whereinthe particle-free conductive ink has a viscosity measured at 25° C. of25 cps or less, such as 20 cps or less.
 14. The method of claim 1,wherein the textile comprises a knit, woven, or nonwoven fabriccomprising fibers of polyester, polyamides, spandex, nylon, Evolon®,elastane, cotton, cellulose, silk, wood, wool, or blends thereof.
 15. Ane-textile produced by the method of claim 1, wherein the e-textilefunctions as a sensor, an electrode, a circuit, an interconnect, alight, an antenna, a resistive heating element, a switch, a battery, orany combination thereof.
 16. An e-textile comprising: a textile havingat least one particle-free conductive trace printed thereon, wherein atleast a portion of the at least one particle-free conductive trace isover-coated with a protective dielectric coating, wherein the at leastone conductive pattern exhibits an ink bleed of less than 0.5 mm, and aresistance of less than 10Ω/□, and wherein the textile comprises a knit,woven, or nonwoven fabric comprising fibers of polyester, polyamides,spandex, nylon, Evolon®, elastane, cotton, cellulose, silk, wood, wool,or blends thereof.
 17. The e-textile of claim 16, wherein theparticle-free conductive trace comprises two or more layers of aparticle-free conductive ink.
 18. The e-textile of claim 16, wherein theat least one particle-free conductive trace exhibits an ink bleed ofless than 0.2 mm, and a resistance of less than 1 Ω/□.
 19. The e-textileof claim 16, wherein the resistance in the conductive trace is increasedby less than 50% after the textile is exposed to 50 wash cycles.
 20. Aresistive heater comprising: a textile having at least one particle-freeconductive pattern printed thereon, wherein at least a portion of theparticle-free conductive pattern is over-coated with a protectivedielectric coating, wherein the resistive heater heats at a rate ofabout 0.7° C./second to about 1° C./second, and wherein resistance inthe conductive trace is increased by less than 50% after the textile isexposed to 50 wash cycles.
 21. The resistive heater of claim 20, whereinthe textile comprises a knit, woven, or nonwoven fabric comprisingfibers of polyester, polyamides, spandex, nylon, Evolon®, elastane,cotton, cellulose, silk, wood, wool, or blends thereof.